This invention relates to the reduction of throttle bore coking in fuel injected motor vehicle engines. Throttle bore coking is a buildup of carbon and possibly other substances on the throttle plate and throttle bore of an engine which can occur on engines provided with port fuel injection: that is, in which the fuel is injected below the throttle bore adjacent the individual combustion chamber inlet valves, so that the throttle bore is not washed with fuel as in throttle body injected engines.
Throttle bore coking can, over time, result in the narrowing of the air passage past a throttle valve which is only slightly open for idle and a resulting lower idle speed. The carbon buildup can be cleaned out during regular engine maintenance by spraying an appropriate cleaner down the throttle bore. Between such cleanings, many idle speed controls can compensate, under normal circumstances, for the narrowing by sensing idle speed and opening the throttle to compensate. However, the degree of throttle opening may not be sufficient for easy cold starts in very cold climates. Additional air passages and/or a hole in the throttle plate may provide additional idle air flow capacity which may be less affected by coking. However, the invention disclosed and claimed herein is an alternative to these measures suitable for many vehicles which does not require expensive design changes to the throttle body or throttle valve.